Over time, we have accumulated a bunch of tools such as our pipeable logic functions to make conditionals flow better, our Oracle module imports nothing but is able to work on all our domain models. And I briefly show what a form wizard and grid (table) can look like.


Alfred is a great helper. One of his best assets is his Alfred.Logic ability.

-- performs conditional validation
    [ ...
    |> Alfred.Logic.when (model.newCreditReference == Types.Yes) ((++) addressValidations)

-- conditionally update models
case msg of
    PersonDetailEdit field ->
            |> Alfred.Logic.when (someCondition field) updateSomeField
            |> PersonDetail.update field

In our quest to turn everything we do into pipes ( things just read alot nicer when the whole function is one declarative data transformation ), we created Alfred.Logic. Full code listing in the glossary.


We have a model helper (named Oracle.elm) that works off common fields and types. Since the backend is mostly constructed via interfaces, our endpoints contains many overlapping fields. Oracle helps to consolidate getter logic in one place:

-- Oracle.elm
type alias HasSurnameFirstName a =
    { a | surname : String, firstName : String }

type alias HasId a =
    { a | id : Maybe Int }

{-| Returns: Jones, Bob ( 123 )
surnameFirstnameId : HasSurnameFirstName (HasId a) -> String
surnameFirstnameId { surname, firstName, id } =
    surname ++ ", " ++ firstName ++ " ( " ++ (id |> toString |> Maybe.withDefault "") ++ " ) "

Oracle is great, it allows us to fetch complex relationships in our data models by specifying the minimal fields required and also allows us to mix and match these type aliases. It also means that the functions are not tied to any particular record and we have a lot of records that repeat fields.

Practically though, we don't actually use this as much as the creator would have wished because the more complex getters typically come with domain logic which looks into our Model folder for logic.

Component Wizardry

I just wanted to show off our 'wizard' component which is great for making specific step-by-step forms that shares one model. Note that the wizard does not hold any parent state but rather, just a list of steps with functions that allows it to go back and forth. It boasts:

  • automatically checks validation on each step
  • conditionally skip steps
  • guaranteed to never get into a invalid step state ( but this is just Elm and ZipList )

Here's the API (Full code listing is also available. May make a package eventually.):

type alias Wizard oz msg =
    { steps : ZipList (Step oz msg)

type alias Step state msg =
    { validStep : state -> Bool
    , init : state -> ( state, Job msg )
    , view : state -> Html msg
    , validate : state -> List String

next : state -> Wizard state msg -> ( Wizard state msg, state, Job msg )
back : state -> Wizard state msg -> ( Wizard state msg, state, Job msg )

init : List (Step state msg) -> Wizard state msg
view : state -> Wizard state msg -> Html msg
makeStep : (state -> Html msg) -> (state -> List String) -> Step state msg
withInit : (state -> ( state, Job msg )) -> Step state msg -> Step state msg
withCondition : (state -> Bool) -> Step state msg -> Step state msg

Used like this:

    [ Wizard.makeStep (viewBase lookup) (always [])
    , Wizard.makeStep (viewNewDependant lookup) validateNewDependant
        |> Wizard.withCondition (...)
    , Wizard.makeStep (viewMemberTransfer lookup) validateMemberTransfer
        |> Wizard.withInit ...a Job
        |> Wizard.withCondition (\state -> ... True/False)

-- on next
case Wizard.validate state wizard of
    [] ->
            ( nextWizard, nextState, job ) =
       state wizard

-- on view
Wizard.view state wizard

So our wizard component holds a bunch of functions. It doesn't hold the steps, this is passed in. Next happens once a step is validated. Steps are conditional, they can contain initial jobs (Cmds + extras). Having a component like this is a massive time saver for multi-stepped forms which we seem to have more of now that there's a wizard.

results matching ""

    No results matching ""